Monday, April 6, 2009
Click the picture for a larger view.
Answer by Tony Leukering
Wow, another single bird, and not a gull, duck, or shorebird!
This week's raptor (and all respondents got at least that far correctly) is perched on the crossarm of a power pole (these poles do NOT carry telephone lines, most of which are buried). Looking at the bird's size relative to the width of the crossarm, the bird is fairly small, say crow-sized or smaller. That enables us to ignore those typical pole-sitters, the large buteos, and a host of other streaky possibilities, leaving us with the following: Mississippi, White-tailed, and Hook-billed kites; Northern Harrier; Sharp-shinned and Cooper's hawks; Broad-winged, Gray, and Red-shouldered hawks; and American and Eurasian kestrels, Merlin, Hobby, and Peregrine and Prairie falcons among the Falconidae.
With so many options to consider, it would be good to find a single feature that can eliminate options in job lots, rather than having to struggle through species-by-species. Well, there are three such features on the bird's head. The first is iris color. While the bird's eyes are partly closed and we might be a bit suspicious that there is not enough eye visible to be sure that we're not seeing just pupil, the fact that the sun is shining and is seemingly fairly bright suggests against that (with bright sun, the pupil should be small, not large). So, with that consideration, the dark right eye should enable us to remove the accipiters. Yeah, two species doesn't quite make a job lot, but....
The second feature on the bird's head that can rule out numerous options, and the most efficient one, is a bit difficult to see. However, enlarging the picture a bunch should enable us to see that the maxilla (upper mandible) has an extra 'tooth' to it. Rather than the cutting edge curving smoothly to the bill's hook, there is a protrusion at the curve that forms an extra bump. This is a feature found, among ABA raptors, only on falcons and is one of the idenifying features of the group.
This brings us to the third feature. Except for the falcon options, all of the species listed above have streaky plumages ONLY when juveniles. If we focus on the bird's cere (the fleshy part at the base of the maxilla), we can see that it is bright yellow. On raptors, the presence of a bright yellow cere is virtually certain proof that the individual is an adult; juveniles have duller ceres, often bluish.
So, not only do we now know that our mystery bird is a falcon, we can also eliminate male American Kestrel and adult Peregrines and Prairies (the latter of which are spotted, not streaked). The pale ground color of the underparts feathers rules out male Eurasian Kestrel. Continuing our perusal of the bird's head, we can see that there is virtually no malar stripe (moustache), a feature so typical of falcons and found on all of our remaining options. Yikes! Then where did we go wrong?
Well, we didn't. Yes, moustaches are a strong feature of most of our options, but it is much weaker on Merlin and the prairie race nearly lacks the feature entirely. As the color of the bird's streaking and crown are both fairly pale for Merlin (suggesting Prairie Falcon), we can use this as confirmatory features of our ID of the bird. I took this picture of an adult female richardsonii Merlin near John Martin Reservoir, Bent Co., CO, on 17 December 2008 during the Christmas Bird Count.
Tallies of incorrect species provided in answers:
Northern Goshawk - 1
Cooper's Hawk - 4
Sharp-shinned Hawk - 2
The 20 of 27 providing the correct answer: